System Update Required for LoZ: BotW

Hey everyone,

I tried to install Cemu, to play LoT:BotW. So far, no problems. But when I run Zelda, theres an Error, named "You must perform a system update to play The Legend of Zelda: Breath of the Wild. Returning to Wii U menu". Has anyone an idea on how to fix this? I haven't found any thread to this, only to update games.
Additionally, I can't press any keys, to click on the "Close" button under the error message. I work with my keyboard and mouse, not with a controller.